1. Field of the Invention
The present invention relates to a multi-wound stainless steel pipe produced by winding a hoop material made of a stainless steel sheet using brazing.
2. Description of the Prior Arts
In general, a multi-wound metal pipe is produced as a product by plastic-deforming a hoop material the surface of which is applied with a Cu brazing material into a multi-wound pipe by a forming apparatus and after melting the Cu brazing material between the walls of the multi-wound pipe by a heating apparatus, solidifying the molten brazing material by a cooling apparatus. In the case of a multi-wound stainless steel pipe, the pipe is generally produced using a stainless steel sheet the surface of which is directly applied with Cu brazing as the hoop material and a multi-wound stainless steel pipe produced using a stainless steel sheet having Ni-brazed layer between the surface of the stainless steel sheet and a Cu-brazed layer is also known.
However, in a conventional multi-wound stainless steel pipe, there are following problems.
That is, when Cu brazing is directly applied onto the surface of a stainless steel sheet, there is a fault that the adhesive force of the stainless steel and Cu is weak and thus the sufficient pressure resisting strength and working strength in the state of being produced as a multi-wound pipe cannot be obtained. Also, when an Ni-brazed layer is formed between the surface of a stainless steel sheet and a Cu-brazed layer, an adhesive force in the sheet state is obtained but there is a problem that in the brazing temperature range after forming multi-wound pipe, the Ni component of the base material of the stainless steel and component of Ni brazing are alloyed with Cu to greatly increase the Ni concentration, which results in lowering the ductility of the brazing material to cause cracking and a releasing phenomenon of the brazing material at terminal working.